The present invention relates to an improved process for the purification of xanthophyll esters from commercially available marigold oleoresin.
The xanthophyll esters in marigold oleoresin predominate in lutein fatty acid esters with varying proportions of the trans- and cis-lutein isomers. The cis-isomers are formed due to exposure of the raw materials to heat, oxygen, and light during processing. The purified lutein ester concentrate with a high proportion of trans-isomers is used in the nutritional supplement industry, such as by being formulated as oil dispersions and beadlets for capsules and tablets. The esters also are used as food colorants and in functional foods.
Unlike free lutein, the lutein ester concentrate is a less expensive ingredient in a highly competitive market. Hence, development of an economical, efficient process for purifying lutein esters has been the focus of a number of patents. In general, the purification of the esters involves use of organic solvent(s) to remove non-xanthophyll impurities, inactive cis-isomers of lutein and also to precipitate or crystallize the xanthophyll esters from the oleoresin. The solvents used generally are lower aliphatic alcohols or ketones. The objective of these publications is to purify the esters to 40% or above containing mainly the trans-lutein esters, suitable for human consumption.
One of the major disadvantages of these processes is the significant reduction in the recovery of the trans-lutein esters during the precipitation step as the esters are lost due to dissolution in the solvents used. Additionally, the processes either use solvents that require special high-cost extraction equipment or very high-quality oleoresin normally not available to small producers who are not backward integrated to the marigold harvest process.
In earlier publications and U.S. Pat. No. 4,048,203, Philip describes purification of the lutein esters by dissolving the oleoresin in lower aliphatic alcohols, preferably isopropanol at 75° C. followed by precipitation at 15° C. to obtain the esters at 51% purity. However, this heat treatment results in an undesirably large proportion of the less-bioavailable cis-lutein isomer in the final product as reported by Levy (U.S. Pat. No. 6,191,203).
Levy discloses a method in U.S. Pat. No. 6,191,293 for the preparation of a trans-lutein esters content at least four times greater and preferably at least nine times greater than the cis-lutein esters content. The lutein esters are extracted from marigold flowers by contacting the corollas with a hydrocarbon solvent. After solvent removal, the crude esters then are mixed with isopropanol at room temperature, preferably at 20° C. where they crystallize off, and the purified esters are collected by filtration. The process provides esters with 40% to 70% purity, but the recovery generally does not exceed 50%-60%. The raw material used also is more purified, as the oleoresin is prepared using corollas, instead of the whole flower head. In the commercial manufacture of the marigold oleoresin, the whole flower head is dried and extracted resulting in the oleoresin with a number of non-xanthophyll impurities. This enriched material is normally not available to small producers.
In order to improve the yield, Quesnel and Flacher (WO 02094772) have disclosed a method of pre-treating the marigold corollas with an alcohol or a nitrile solvent for a time sufficient to extract any non-xanthophyll compounds, followed by extraction of the remaining raw material with a hydrocarbon solvent for a sufficient time to extract the xanthophyll esters. The reported recovery was up to 100% with a purity of 54%-65%. The process, however, requires a change in the commercial production practices for the manufacturers of the marigold flower meal and the oleoresin, which, based on the market potential for the esters is not a practical option.
U.S. Pat. No. 6,737,535 discloses the use of aliphatic ketones for the purification of the commercially available marigold oleoresin. The oleoresin is admixed with the solvent at a ratio of 1:3 to 1:15 and stirred for preferably around 10 hr at a temperature in the range of 15°-30° C. The precipitated lutein esters are separated by filtration, washed with fresh solvent, and dried under vacuum at room temperature. The use of highly volatile solvents with long extraction time, filtration, and washing steps makes this process uneconomical and unattractive due to safety concerns and the need for increased capital expenditure for special extraction equipment.
U.S. Patent Publication 2003/0130531 discloses a multiple step process for the purification of the xanthophylls esters to not less than 70% purity. The oleoresin is dissolved in acetone at 50° C., cooled to 20° C. and the precipitated material is filtered off. The acetone is removed under reduced pressure to obtain an acetone soluble concentrate. The concentrate is further dissolved in n-butanol at 45° C., cooled to 4° C. to remove an n-butanol soluble impurity with or without the addition of water or lower alcohols such as methanol or ethanol. The precipitate is separated by filtration and mixed with excess of ethanol, dispersed and then separated by filtration, followed by drying under vacuum. The multiple steps involved make this process economically not feasible.